organic compounds that contain oxygen or sulfur three families of compounds that contain a c atom...

Organic Compounds that Contain Oxygen or Sulfur

Three families of compounds that contain a C atomsingly bonded to O or S are:

1. Alcohols, which contain an OH (hydroxyl) group

2. Ethers, which have two alkyl groups bonded to an O atom

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Organic Compounds that Contain Oxygen, Halogen, or Sulfur

3. Alkyl halides, which contain a halogen atom, (X= F, Cl, Br, or I) bonded to a tetrahedral carbon.

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4. Thiols, which contain a SH (sulfhydryl) group.

Organic Compounds that Contain Oxygen, Alkyl Halides, or Sulfur

Two families of compounds that contain a carbonyl group C=O:

1. Aldehydes, which have at least one H atom bonded to the carbonyl carbon.

2. Ketones, which have two alkyl groups bonded to the carbonyl carbon.

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Structure and Properties of Alcohols

• Alcohols contain a hydroxyl (OH) group.

• Alcohols are classified by the number of C atoms bonded to the C with the OH group.

A primary (1o) alcohol hasan OH group on a C bondedonly to 1 C atom.

1o4


A secondary (2o) alcohol hasan OH group on a C bondedonly to 2 C atoms.

2o

3o

A tertiary (3o) alcohol hasan OH group on a C bondedonly to 3 C atoms.

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• An alcohol (ROH) contains an O atom with a bent shape like H2O and a bond angle similar to a tetrahedral.

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• Alcohols have an H atom bonded to an O atom, making them capable of intermolecular hydrogen bonding.

• This gives alcohols much stronger intermolecular forces than hydrocarbons.


• As a result, alcohols have higher boiling and melting points than hydrocarbons of comparable molecular weight and shape.

stronger intermolecular forceshigher boiling and melting point

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melting point: -138 ºCboiling point: -0.5 ºC

melting point: -127 ºCboiling point: 97 ºC


• Alcohols are soluble in organic solvents.

• Low molecular weight alcohols (6 Cs or less) are soluble in water.

• Higher molecular weight alcohols (6 Cs or more) are not soluble in water.

2 Cs in chainwater soluble

8 Cs in chainwater insoluble

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Nomenclature of Alcohols

• Find the longest carbon chain containing the carbon bonded to the OH group.

• Number the carbon chain to give the OH group the lower number, and apply all other rules of nomenclature.

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In the IUPAC system, alcohols are identified by the suffix -ol.

To name an alcohol:


Give the IUPAC name of the following alcohol.

Step [1]Find the longest carbon chain containing theC bonded to the OH group.

5 Cs in longest chain

pentane ----> pentanol

• Change the –e ending of the parent alkane to the suffix –ol.

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Sample Problem 12.2


Step [2] Number the carbon chain to give the OH groupthe lower number, and apply all other rulesof nomenclature.

1-pentanol Answer

3,3-dimethyl-1-pentanol

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• When an OH group is bonded to a ring, the OH is automatically on C1.

• The “1” is usually omitted from the name.

• The ring is then numbered to give the next substituent the lower number.

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Structure and Properties of Ethers

• Ethers (ROR) have two alkyl groups bonded to an O atom.

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• The O atom of an ether has a bent shape like H2O and a bond angle similar to a tetrahedral.

Naming Ethers

Simple ethers are usually assigned common names:

• Name both alkyl groups bonded to the O atom.

• Arrange these names alphabetically.

• Finally, add the word “ether” to the end.

CH3 O CH2CH3

methyl ethyl

ethyl methyl ether

CH3CH2 O CH2CH3

ethyl ethyl

diethyl ether

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• For identical alkyl groups, add the prefix di-.

Structure and Properties of EthersPhysical Properties

• Ether has two polar C—O bonds with a bent shape, therefore it has a net dipole.

• Ether does not contain an H atom bonded to an O atom, so ether cannot form intermolecular hydrogen bonds.

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These facts give ethers:

As a result, ethers of comparable size and shapetend to have:

• stronger intermolecular forces than alkanes.

• weaker intermolecular forces than alcohols.

• higher melting and boiling points than hydrocarbons.

• lower melting and boiling points than alcohols.

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• Ethers are soluble in organic solvents.

• Low molecular weight ethers (5 Cs or less) are soluble in water, as water can hydrogen bond to the ether’s O atom.

• Higher molecular weight ethers (6 Cs or more) are not soluble in water. 18

Focus on Health & MedicineEthers as Anesthetics

• A general anesthetic is a drug that interferes with nerve transmission in the brain, resulting in a loss of consciousness and the sensation of pain.

• Modern variations include the three ethers below:

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• Diethyl ether was first demonstrated as an anesthetic in the nineteenth century.

Reactions of AlcoholsDehydration

• Dehydration is the loss of H2O from a starting material.

• It occurs when an alcohol is treated with a strong acid like H2SO4, and forms an alkene product.

• Dehydration is an example of an elimination reaction, in which parts of the starting material are “lost” and a multiple bond is formed.

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Reactions of AlcoholsDehydration

• Examples:

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Reactions of AlcoholsOxidation

Oxidation results in a(n):

• increase in the number of C—O bonds.

• decrease in the number of C—H bonds.

The symbol [O] indicates an oxidation reaction.

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• Oxidation occurs by replacing the C—H bonds on the carbon bearing the OH group by C—O bonds.

• All oxidation products from alcohol starting materials contain a C=O, a carbonyl group.

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• Primary (1o) alcohols first oxidize to aldehydes (RCHO), replacing 1 C—H with 1 C—O.

• Aldehydes are further oxidized to carboxylic acids (RCOOH), replacing 1 C—H with 1 C—O.

1o alcohol(ROH)

aldehyde(RCHO)

carboxylic acid(RCOOH)

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• Secondary (2o) alcohols are oxidized to ketones (R2CO) replacing 1 C—H with 1 C—O.

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• Tertiary (3o) alcohols have no H atoms on the C with the OH group, so they are not oxidized.

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• The oxidation of ethanol with K2Cr2O7 was the first available method for the routine testing of alcohol concentration in exhaled air.

Focus on The Human BodyOxidation and Blood Alcohol Screening

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• Oxidation with K2Cr2O7 is characterized by a color change, as the red-orange reagent is reduced to a green Cr3+ product.

Focus on Health & MedicineThe Metabolism of Ethanol

• When ethanol is consumed it is quickly absorbed in the stomach and small intestines.

• In the liver, the enzymes alcohol and aldehyde dehydrogenase act as oxidizing reagents.

CH3CH—OH

ethanol

[O]

CH3 HC

O

acetaldehyde

[O]

CH3 OHC

O

acetic acid

• Consuming more ethanol than can be metabolized leads to a buildup of acetaldehyde, which is toxic.

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Organic Compounds that Contain Alkyl Halides

• Alkyl Halides contain a halogen atom (X= F, Cl, Br, or I) bonded to a tetrahedral carbon.

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• Alkyl halides are classified by the number of C atoms bonded to the C with the halogen.

Structure and Properties of Alkyl Halides

• Alkyl halides contains a polar C–X bond, but are incapable of hydrogen bonding.

• boiling point and melting point increase with the size of the alkyl group due to increased surface area.

• boiling point and melting point increase with the size of the halogen.

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For an alkyl halide, the…

Structure and Properties of Alkyl Halides

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Nomenclature of Alkyl Halides

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HOW TO Name an Alkyl Halide

ExampleGive the IUPAC name of the following alkyl halide:

Step [1] Find the longest chain containing the halogen.

Nomenclature of Alkenes and Alkynes

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HOW TO Name an Alkene or Alkyne

Step [2] Apply all other rules of nomenclature.

Organic Compounds that Contain Sulfur

• Thiols contain a sulfhydryl group (SH) bonded to a tetrahedral carbon.

• Because S is just below O on the periodic table, thiols are similar to alcohols.

• Thiols have a bent shape around the S atom.

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• However, thiols contain no O—H bonds, so they are incapable of intermolecular hydrogen bonding.

• This gives thiols lower boiling and melting points than similar alcohols.

CH3CH2—OHethanol

bp 78 oC

CH3CH2—SHethanethiol

bp 35 oC

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• Thiols have a characteristic foul odor (skunk, onions, etc.)

• They can be oxidized to disulfides.

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• The disulfides can be converted back to thiols with a reducing agent.

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• The symbol for a general reducing agent is [H], since hydrogen atoms are often added during reduction.


• To make straight hair curly, the disulfide bonds holding the hair proteins together are reduced.

• The hair is then turned around curlers, and an oxidizing agent is applied.

• This re-forms the disulfide bonds in the hair, now giving it a curly appearance.

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Aldehydes and KetonesStructure and Properties of Aldehydes and

Ketones

Two families of compounds contain a carbonyl group:

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Aldehydes (RCHO) Ketones (RCOR or R2CO)

• The carbonyl carbon atom is trigonal planar, with bond angles of 120o.

• O is more electronegative than C, so the carbonyl group is polar.

• The carbonyl C is e− rich (δ−) and the carbonyl O is e− poor (δ+).

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Aldehydes and KetonesStructure and Properties of Aldehydes

and Ketones

NomenclatureNaming Aldehydes

To name an aldehyde using the IUPAC system:

• Find the longest chain containing the CHO group.

• Change the “-e” ending of the parent alkane to “-al.”

• Number the chain to put the CHO group at C1, but omit “1” from the name.

• Apply all other nomenclature rules.

CH3CHCH

CH3

CH3

C

O

H

butane butanal

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Answer:2,3-dimethylbutanal

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NomenclatureNaming Aldehydes

Common names are used for simple aldehydes;the names contain the suffix “-aldehyde.”

formaldehyde acetaldehyde benzaldehyde

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NomenclatureNaming Ketones

To name a ketone using the IUPAC system:

• Find the longest chain containing the carbonyl group.

• Number the chain to give the carbonyl carbon the lower number.

• Apply all other nomenclature rules.

CHCH2CH3CH3

CH3

C

O pentane pentanone

• Change the “-e” ending of the parent alkane to “-one.”

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Answer:3-methl-2-pentanone

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• With cyclic ketones, numbering begins at the carbonyl carbon, “1” is omitted from the name.

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• The ring is then numbered clockwise or counterclockwise to give the first substituent the lower number.

Name the ring.

cyclohexane cyclohexanone

Sample Problem 12.7

Step [1]


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Number and name the substituents, making the C=O C1.

Sample Problem 12.7

Step [2]

1

3

43-ethyl-4-methylcyclohexanone

Answer:

Physical Properties

Aldehydes and ketones have higher boiling pointsthan similar hydrocarbons because:

• They are polar molecules.

• They have stronger intermolecular forces than alkanes and alkenes.

Increasing boiling pointIncreasing boiling point

CH3CH2CH2CH2CH3

pentanebp 36 oC

CH3CH2CH2CHObutanalbp 76 oC

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Physical Properties

Aldehydes and ketones have lower boiling pointsthan similar alcohols because:

• They do not have an O—H bond.

• Therefore, they cannot have intermolecular hydrogen bonding.

• Thus, they have weaker intermolecular forces than alcohols.

Increasing boiling pointIncreasing boiling point

CH3CH2COCH3

2-butanonebp 80 oC

CH3CH2CH2CH2OH1-butanolbp 118 oC

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Physical Properties

• Aldehydes and ketones are soluble in organic solvents.

• Those molecules with less than 6 Cs are soluble in both organic solvents and water.

• Those molecules with 6 Cs or more are soluble in organic solvents, but insoluble in water.

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Focus on Health & MedicineInteresting Aldehydes and Ketones

Cinnamaldehyde, the major component ofcinnamon bark:

Vanillin, the primary component of the extract of thevanilla bean:

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Oxidation of Aldehydes

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Aldehydes contain a hydrogen atom bonded directly to the carbonyl carbon; they can be oxidized to carboxylic acids:

Reactions of Aldehydes and KetonesOxidation of Aldehydes

In oxidation, the aldehyde C—H bond is convertedinto a carboxylic acid C—OH bond.

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Ketones cannot be oxidized because there is noC—H bond.

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Aldehydes can be selectively oxidized in the presenceof other functional groups using the Tollens reagent.

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Stereochemistry is the 3-dimensional structure of compounds.

• The cis and trans examples below are stereoisomers.

Looking Glass ChemistryMolecules and Their Mirror Images

Stereoisomers differ only in the 3-dimensional arrangement of atoms.

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Molecules and Their Mirror ImagesWhat It Means to be Chiral or Achiral

• Left hands and right hands are mirror images of each other.

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• Left and right hands are not identical (nonsuperimposable).

• A molecule that is not superimposable on its mirror image is chiral.

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• Two socks from a pair are mirror images that are superimposable.

• A molecule that is superimposable on its mirror image is achiral.

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Molecules and Their Mirror ImagesThe Chirality of Molecules

To determine whether a molecule is chiral or achiral we must examine what groups are bonded to each carbon atom:

• A chiral molecule has at least one carbon atoms bonded to four different groups.

To superimpose a molecule and its mirror image you can perform any rotation but you cannot break bonds.

• An achiral molecule does not contain a carbon atom bonded to four different groups.

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• For CH2BrCl:

• Rotate the molecule to align bonds:

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• For CHBrClF:

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• The two mirror images of CHBrClF are enantiomers, mirror images that are not superimposable.

• A carbon atom with four different groups like CHBrClF is called a chirality center.

• A molecule that is not superimposable on its mirror image is a chiral molecule.

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Chirality CentersLocating Chirality Centers

• To locate a chirality center, look at each tetrahedral C atom in a molecule.

• Look at the four groups—not the four atoms— bonded to it.

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• We consider all atoms in a group as a whole unit.

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• Chirality centers in the examples below are labeled in red:

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Fischer Projections

A Fischer Projection takes a 3-D tetrahedral shape, and re-draws it.

• A carbon atom is located at the intersection.

• The horizontal bonds come forward, on the wedges.

• The vertical bonds go back, on the dashed lines.

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Fischer Projections• We can draw the cross and Fischer projection for both enantiomers of 2-butanol:

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Focus on Health & MedicineChiral Drugs

• Many drugs are chiral, and often they must interact with a chiral receptor to be effective.

• One enantiomer of a drug may be effective in treating a disease whereas its mirror image may be ineffective.

• One enantiomer may “fit” the chiral receptor and evoke a specific response.

• Its mirror image may not fit the same receptor, making it ineffective.

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Focus on Health & MedicineChiral Drugs

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Focus on Health & MedicineChiral Pain Relievers

• Ibuprofen is an active anti-inflammatory agent whose enantiomer is inactive, and is sold as a racemic mixture.

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Focus on Health & MedicineParkinson’s Disease and L-Dopa

• L-Dopa, a dopamine precursor, is used to help treat the dopamine deficient brains of Parkinson’s patients.

• Dopamine cannot be directly taken by a patient because it cannot cross the blood-brain barrier.

organic compounds that contain oxygen or sulfur three families of compounds that contain a c atom...

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